Binder compound

ABSTRACT

The present invention relates to a binder compound based on natural oil, polymer and resin. Such binder compounds can for example be used in roof covering membranes as an environmentally friendly alternative to bituminous roof covering membranes.

The present invention relates to a binder compound based on natural oils, polymer and resin.

Such binder compounds can for example be used for production of roof covering membranes and similar as an environmentally friendly alternative to bituminous roof covering membranes.

In construction or road building, traditional products of bituminous and petrochemical origin are used as constituents of membranes such as roof covering membranes or as a basis for asphalt. Traditionally bitumen is a by-product of the petrochemical industry which offers a cheap and high quality raw material for the production of roof covering membranes or asphalt. Due to rising demand for petroleum products for use in chemistry and as fuel, the quality and availability of high quality bitumen has diminished greatly. Also the use of bituminous products has a harmful influence on the environment as its production causes great environmental pressure. Another disadvantage of the use of bitumen is the acidification of rain water as a result of interaction of UV and bitumen.

WO 2009/071653 describes a compound which consists of resin of vegetable origin, oil of vegetable origin and a polymer that contains functional groups selected from the carboxylic acid anhydride, carboxylic acid and epoxide groups. The disadvantage of this compound is that only such functionalized polymers can be used, which entails a restriction in suitable polymers and in addition increases the cost price of this compound.

The object of the present invention is to provide a binder compound in which oil of natural origin, resin and polymer are used, while allowing a wider choice of polymer.

The above object is achieved by a binder compound comprising:

-   -   natural oil in a quantity of 14-19 w.%; and     -   polymer in a quantity of 4 to 17 w.% and selected from the group         consisting of styrene-butadiene-styrene (SBS),         styrene-ethylene-butadiene-styrene (SEBS),         styrene-isoprene-styrene (SIS), polyisobutylene (PIB),         polyhydroxybutyrate, polylactide (PLA), polyolefins, polyamides,         polyesters, atactic polypropylene (APP) and isotactic         polypropylene (IPP) and combinations thereof, wherein said         polymer contains no functional groups selected from a carboxylic         acid anhydride group, a carboxylic acid group and an epoxy         group; and     -   resin in a quantity of 32 to 40 w.%.

Such a binder compound offers the advantage that it is an environmentally friendly alternative to binder compounds based on bitumen as it contains natural oil which is a source of renewable carbon and therefore has little or no influence on the CO2 balance in the atmosphere. Another important benefit is that the problem of acid leaching, which can lead to acidified rain water, is avoided because natural oil does not lead to acidification under the effect of UV. As a result the recovered rain water can be used with less further treatment for sanitary or other applications. Another benefit is that the roof covering membranes and cold adhesives which contain the binder compound according to the invention can be processed, applied or used in the same way as bituminous roof covering membranes and cold adhesives.

Thanks to the interaction between natural oil, resin and polymer in this concentration range of natural oil, the binder compound has the following viscosity, namely a viscosity of 1400 to 25000 Pa·s at 180° C. This viscosity is similar to the viscosity of modified bitumen binder compounds. Due to this viscosity the binder compound will be solid at an ambient temperature of approximately −15° C. to approximately 40° C., which is necessary for example for the setting and hardness of roof covering membranes and cold adhesives containing the binder compound. At ambient temperatures above around 25° C. the binder compound also remains cohesive and will consequently not flow out, which again is favorable for use in roof covering membranes and road construction.

Thanks to the interaction between natural oil, resin and polymer in this concentration range of natural oil, the binder compound also has a relatively low liquefaction temperature, namely 100 to 180° C. This is the temperature at which the binder compound acquires a specific degree of plasticity as defined in the profession by the technical standard ASTM D36/D36M-09 of Dec. 15, 2009. The binder compound must be sufficiently plastic when for example it forms part of a roof covering membrane which is applied to a substrate or surface by means of burner lances, because this achieves a good adhesion of the roof covering membrane to the substrate. Burner lances typically use a flame with a flame temperature of 180 to 220° C. At this liquefaction temperature, the binder compound will already be sufficiently plastic in the range of 100 to 180° C., in contrast to bituminous binder compounds which typically have a higher liquefaction temperature, namely higher than 180° C., whereby the flame lances can heat up more quickly and use less energy, which protects the environment and saves costs.

Thanks to the presence of polymer, the binder compound has adequate stability, cohesion and cold flexibility. Cold flexibility is defined in the industry as the temperature (° C.) at which the roof covering membrane breaks on flexion. A cold flexibility of −9 to −40° C. has the benefit that even at extremely low ambient temperatures, e.g. down to −40° C., no breakage of the binder compound will occur. This applies both to a freshly produced binder compound and to an aged binder compound, for example after a life of twenty years during which great fluctuations in ambient temperature have occurred. Adequate cold flexibility will for example also allow a product, e.g. a roof covering membrane, containing the binder compound to be rolled at an ambient temperature of −40° C. e.g. for stacking, storage or transport, and then unrolled again or applied without the binder compound breaking.

The resin together with the natural oil ensures the formation of a cohesive whole. In a preferred embodiment the resin is a natural resin. In another preferred embodiment the resin is a synthetic resin.

It is in any case known that a binder compound forms a better cohesive whole if resin is added to natural oil. However by use of the binder compound according to the present invention, even with a much lower quantity of resin, a better viscosity namely from 1400 to 2500 Pa·s, better cold flexibility namely from −9 to −40° C., can be achieved than in known binder compounds. In fact where WO2009/071653 in its specific examples mentions resin concentrations of 77 w.% and 80 w.%, the binder compound according to the present invention has a resin quantity of maximum 70 w.%. This reduces the cost price of the binder compound.

The binder compound can form part of other products which as a result acquire an environmentally friendly and renewable aspect and long term stability.

The binder compound according to the present invention is preferably used in production of a roof covering membrane which gives such roof covering membranes favorable properties such as for example ease of handling and processing, and furthermore can also be rolled up or installed, remains crack-free and stable even if the binder compound reaches a low temperature e.g. −40° C. In winter the binder compound which forms part of such roof covering membranes will consequently not tend to break or crack. Such roof covering membranes furthermore have a viscosity of 1400 to 25000 Pa·s at 180° C. so that the roof covering membrane can be processed easily and remains stable even if the binder compound reaches a high temperature e.g. 80° C. Another important advantage is also that this viscosity falls within the range of viscosities of bituminous roof membranes available on the market, which makes for ease of use by the skilled person. In summer the binder compound which forms part of such roof covering membranes will consequently not tend to melt at an ambient temperature of 35° C. Such a roof covering membrane is water-tight, durable and stable and has a high cracking and perforation resistance.

Such a roof covering membrane is ecologically responsible as less non-renewable CO2 occurs because the raw materials are mainly renewable. In addition such a roof covering membrane is halogen-free and 100% recyclable. It can be attached in combination with a cold adhesive according to the present invention which creates an ecological roof covering.

The binder compound according to the present invention can furthermore preferably be used in the production of a road surfacing compound which contains the binder compound in a quantity of 1 to 20 w.%, more specifically in a quantity of 10 to 15 w.%, more specifically in a quantity of 1 to 10 w.%, yet more specifically in a quantity of 1 to 7 w.%, and an aggregate or filler. Such road surfacing compounds form an environmentally friendly alternative to asphalt and other bituminous surfaces.

The binder compound according to the present invention is preferably also used in other applications such as the production of a watery emulsion. In a preferred embodiment the watery emulsion according to the invention is characterized in that it contains the binder compound in a quantity of 40 to 70 w.%, water in a quantity of 60 to 30 w.% and an emulsifier in a quantity of 3 to 10 w.%. Such watery emulsions offer the advantage that they can form part of paints and coatings.

Also the binder compound according to the present invention can be used for cold adhesive compounds. In a preferred embodiment the cold adhesive compound according to the invention is characterized in that it contains the binder compound in a quantity of 25 to 70 w.%, more specifically a quantity of 40 to 50 w.%, and one or more solvents or vegetable oils or derived from vegetable oils, or a combination thereof, in a quantity of 7 to 25 w.% and a filler in a quantity of 25 to 35 w.%. Such cold adhesive compounds offer the advantage that they are an environmentally friendly alternative to conventional cold adhesive compounds based on bitumen.

More details and features of the invention arise from the description given below and with reference to the enclosed drawing.

FIG. 1 is a graph which shows viscosity as a function of time during preparation of the binder compounds from example 5 with (+) and without (O) antioxidant, and a bituminous binder compound (x).

The examples are directed amongst others at binder compounds and roof covering membranes but it will be clear that the binder compound according to the present invention can also be used in other fields such as for example in road surfacing, cold adhesive, coatings, paints, textiles and the carpet industry.

As used here, the term “natural oil” refers to an oil derived from vegetable or similar sources. The term “natural oil” comprises natural oil derivatives unless specified otherwise. Examples of natural oils comprise but are not limited to vegetable oils, algae oils, fish oils, animal fats, tall oils, distillation fractions of these oils, derivatives of these oils such as fatty acids and fatty acid alkyl (e.g. methyl) esters, combinations of one or more of these oils and similar. As used here, the term “natural oil derivatives” refers to compounds or a mixture of compounds derived from natural oil using a method or a combination of methods known in the chemical industry. These methods comprise saponification, esterification, hydrogenation (partial or complete), isomerization, oxidation and reduction.

The binder compound according to the invention comprises natural oil in a quantity of 0.1 to 25 w.%, more specifically a quantity of 14 to 19 w.%. The natural oil for use in the binder compound comprises for example fatty acids e.g. C₆ to C₂₄ fatty acids, esterified fatty acids, triacylglycerols or fatty alcohols. These natural oils offer the advantage that they show good and sustained interaction with resin and polymer so that a cohesive whole is achieved. In the quantity selected, also the natural oil does not leak or leach out of the binder compound.

Preferred examples of vegetable oils are canola oil, rapeseed oil, coconut oil, maize oil, cottonseed oil, olive oil, palm oil, peanut oil, safflower oil, sesame oil, soya oil, sunflower oil, linseed oil, palmpit oil, tung oil, jatropha oil and castor oil. Preferred examples of animal fats are for example lard, tallow, chicken fat, suet and fish oil. Tall oils are by-products from the production of wood pulp. Preferred examples of natural oil derivatives comprise gums, phospholipides, soap stock, acidified soap stock, distillate or distillate slurry, fatty acids and fatty acid alkyl (e.g. methyl) esters of natural oil. For example the natural oil derivative can be a fatty acid methyl ester (FAME) derived from the glyceride of the natural oil.

Preferably the natural oil contains canola or soya oil or refined, bleached and deodorized soya oil. Soya oil consists of unsaturated polyesters of glycerol e.g. saturated fatty acids e.g. palmitic acid and stearic acid, and unsaturated fatty acids e.g. oleic acid, linoleic acid and linolenic acid, with around 95 w.% or higher (e.g. 99 w.% of higher) triglycerides of fatty acids. In a particular embodiment crude tall oil pitch (CTO pitch), a waste stream from the paper industry, is used as the source of tall oil fatty acids and natural resins. The use of CTO pitch offers an ecological benefit because this reuses a waste stream as a “second generation” renewable raw material and consequently less “first generation” renewable natural oil and resin is required.

The present invention relates to a binder compound which furthermore also comprises polymer in a quantity of 0.1 to 40 w.%, more specifically a quantity of 3 to 20 w.%, even more specifically a quantity of 4 to 17 w.%, and selected from the group comprising SBS, SEBS, SIS, PIB, polyhydroxybutyrate, PLA, polyolefins, polyamides, polyesters, APP and IPP and combinations thereof.

U.S. Pat. No. 7,670,420 describes a compound which consists of vegetable oil and resin of vegetable origin. This compound however does not contain a polymer which means the softening point lies between 30° C. and 75° C., which is very low. This has the consequence that this compound has a tendency to melt at a temperature above 75° C. which makes this compound less suitable as a membrane e.g. a roof covering membrane, or as a bituminous cold adhesive on roofs which are exposed to high temperatures as a result of sunlight. The softening point of the binder compound in the present invention is however between 75° C. and 145° C., which makes it suitable for use as a roof covering membrane.

The use of polymers in the binder compound will ensure a good cold flexibility, good liquefaction properties and good viscosity. SBS is a suitable choice in binder compounds because it mixes well during production of the binder compound and gives the best result in relation to cold flexibility, liquefaction properties and viscosity.

Functionalized polymers such as described in WO 2009/071653 are not used.

Examples of polyolefins which are used as polymers in the binder compound are polyethylene and polypropylene. An example of polyesters which are used as polymers in the binder composition is polyethyleneterephthalate.

The present invention relates to a binder compound which furthermore also comprises resin in a quantity of 0.1 to 70 w.%, more specifically in a quantity of 20 to 50 w.%, even more specifically in a quantity of 32 to 40 w.%. As resin both natural and synthetic resins can be used. Examples of natural resin are gum resin and derivatives of gum resin such as esters of gum resin, esters of dehydrogenated gum, resin esters of stabilized gum resin, esters of resin acids, esters of stabilized resin acids, esters of polymerized gum resin, phenolic modified esters of gum resin, pentaerythritol esters of gum resin, triethylene glycol esters of gum resin, ethylene glycol esters of gum resin, dibasic acid modified gum resin, resin oil, cardanol and other products derived from the oil of cashew nut shells (CNSL or cashew nut shell liquid), furan resins and products derived from furan resins. Synthetic resins can be both amorphous and crystallized

In a preferred embodiment the binder compound according to the invention is characterized in that it comprises an antioxidant e.g. a phenolic antioxidant suitable for preventing oxidation of the binder compound, more particularly the polymer in combination with the resin. As a result the viscosity and cohesion of the binder compound are retained. In a further preferred embodiment the binder compound contains an antioxidant in a quantity of 0.1 to 3 w.%, more specifically 0.5 to 1.5 w.%.

Preferably the binder compound comprises a filler in a quantity of less than 65 w.%, more specifically in a quantity of 20 to 50 w.%, even more specifically in a quantity of 32 to 40 w.%. The high content of filler than usual in conventional bitumen-based binder compounds can be used because of the good cold flexibility of the binder compound and also entails an economic benefit. All fillers for use in bitumen-based binder compounds can be used in the binder compound according to the present invention. Examples of fillers are talcum, CaCO₃, sand, silica, stone powder, fly ash, limestone powder, slaked lime, organic fillers such as flour, meal, sawdust and cork powder. The filler ensures amongst others that the binder compound is less sticky. Also the filler is normally the cheapest component which gives the binder compound an economic advantage.

In a particular embodiment the binder compound contains a flame retarder such as e.g. ATH (aluminum trihydrate) or colmanite, whereby the binder compound and products which contain the binder compound such as roof covering membranes are more fire-resistant.

In another preferred embodiment the binder compound contains coloring or colorings e.g. organic or inorganic pigments such as TiO₂, Fe₂O₃ whereby the binder compound can assume a color depending on the choice of coloring or colorings.

The present invention also relates to a roof covering membrane comprising the binder compound according to the present invention. In a particular embodiment the roof covering membrane comprises a reinforcement. As reinforcement a glass fleece or a polyester e.g. a non-woven polyester can be used. One or more reinforcements can be used. In a preferred embodiment the roof covering membrane comprises a glass fleece and a non-woven polyester. These give the membrane a dimensional stability and good resistance to cracking and perforation. In a preferred embodiment the roof covering membrane comprises a coated reinforcement along one or more sides. This reinforcement can be coated with a polymer coating e.g. a coating of acrylate or another polymer such as PIB or PE. This coating ensures that the natural oil does not migrate to the surface of the roof covering membrane and then leach out. This coating can also be a reflective coating which reflects sunlight e.g. by the presence of metal particles such as e.g. TiO₂.

In another preferred embodiment one or more sides of the roof covering membrane are covered with talcum or a polymer film (PE, PP, etc.) so that roof covering membranes which comes into contact with each other, e.g. when rolled onto a roll, do not stick together. In contrast to the polymer film, the talcum need not be removed before the roof covering membrane is applied to the substrate. The roof covering membrane with talcum can therefore be applied directly to the substrate using cold adhesive, flame or hot air.

In a preferred embodiment a layer of chippings, e.g. slate chippings or slate chippings mixed with red or black coloring, can be applied to the surface of the roof covering membrane to give the roof covering membrane the desired appearance.

The present invention also relates to a road surfacing compound comprising the binder compound according to the present invention in a quantity of 1 to 20 w.%, more specifically a quantity of 10 to 15 w.%, more specifically a quantity of 1 to 10 w.%, even more specifically a quantity of 1 to 7 w.%, and an aggregate. As an aggregate, for example but without limitation, quartzite or limestone can be used.

The present invention also relates to a watery emulsion comprising the binder compound according to the present invention in a quantity of 40 to 70 w.%, water in a quantity of 60 to 30 w.% and an emulsifier in a quantity of 3 to 10 w.%. As an emulsifier for example surfactants can be used.

The present invention also relates to a cold adhesive compound comprising the binder compound according to the present invention in a quantity of 25 to 70 w.%, more specifically a quantity of 40 to 50 w.%.

The present invention also relates to a cold adhesive compound which furthermore comprises one or more solvents or natural oils or derivatives of natural oils or a combination thereof in a quantity of 7 to 25 w.%. As solvents in the cold adhesive compound for example naphtha, petrol or white spirit can be used. As natural oils or derivatives of natural oils in the cold adhesive compound, fatty acids, triacyclgycerol, fatty acid esters, fatty alcohols can be used.

The present invention also relates to a cold adhesive compound which furthermore contains a filler in a quantity of 25 to 35 w.%. As a filler in the cold adhesive compound, inorganic and organic fillers such as calcium carbonate and cellulose fibers can be used.

The present example also relates to a method for preparation of a binder compound according to the present invention. The method is characterized by mixing at high temperature e.g. higher than or equal to 150° C. This has the benefit that the mixing can take place quickly and efficiently, a stable binder compound is achieved and less heat energy is required than for the production of a bituminous binder compound, which typically takes place at 180 to 200° C.

EXAMPLES Example 1 Ingredients (w.%) of Binder Compounds

Quantity (w. %) SBS 11 10.6 Sunflower oil 16 15.4 Colophonium resin 38 0 Pentaerythritol gum resin 0 36.6 CaCO₃ filler 35 29 Pigments 0 5

These binder compounds, produced by mixing at 150° C., had a viscosity of around 3000 Pa·s and were therefore particularly suitable for use in “self-adhesive” roof covering membranes. These self-adhesive roof covering membrane could be applied to a roof by simply lightly warming to 100° C. either with hot air or with a gentle flame. These self-adhesive roof covering membranes were fitted with a polymer film to prevent layers on a roll from sticking together. This polymer film is removed before application.

Example 2 Ingredients (w.%) of a Binder Compound

Quantity (w. %) SBS 12.5 Sunflower oil 17.5 Pentaerythritol gum resin 34 CaCO₃ filler 34 Pigments 5 Antioxidant 1

This binder compound, produced by mixing at 150° C., had a viscosity of around 14000 Pa·s and was therefore particularly suitable for use in roof covering membranes or carpets.

Example 3 Ingredients (w.%) of a Binder Compound

Quantity (w. %) SBS 11 Crude tall oil pitch 25 Pentaerythritol gum resin 27 CaCO₃ filler 37

The crude tall oil pitch contained 65% fatty acids and tall oil at 35% colophonium resin. The use of crude tall oil pitch offered an economic benefit as consequently less resin needed to be added to the binder compound. With a viscosity of around 3000 Pa·s the binder compound was particularly suitable for use in watery emulsions or cold adhesives.

Example 4 Ingredients (w.%) and Physical Properties of Binder Compounds

Quantity (w. %) SBS 11.5 11.5 Fatty acids of linseed oil 18.3 18.3 Pentaerythritol gum resin 31.8 31.8 CaCO₃ filler 33.9 32.9 Antioxidant 1.5 1.5 Flame-retarder 4.5 3 Properties Softening point (° C.) 108-145 114-137 Viscosity at 180° C. (Pa · s) 17150 11775 PEN at 25° C. ( 1/10 mm) 51 61 PEN at 60° C. ( 1/10 mm) 98 109 Cold flexibility (° C.) initial −32 −24 after 7 d at 70° C. −22 −16 after 28 d at 70° C. −17 −9

Thanks to the high viscosity and low PEN, these binder compounds are suitable for use as roof covering membranes or road surfacing compounds.

Example 5 Production of Binder Compounds on Industrial Scale

To produce the binder compound on an industrial scale, in particular in large volumes, the following production method is used. Resin, oil and SBS are mixed for a few hours at 180° C. As a filler, CaCO₃ is added. This binder compound (table 1, column 1) showed a reduction in viscosity during mixing (FIG. 1). As a result the binder compound is suitable for use in watery emulsions or cold adhesives.

To prevent thermally induced oxidation of the polymer, according to this method a binder compound was produced with antioxidant (table 1, column 2), namely a phenolic antioxidant (Irganox). This binder compound largely retained its viscosity during the mixing process (FIG. 1) thanks to the presence of the antioxidant and is therefore ideally suited for use in roof covering membranes or carpets. The viscosity was comparable to the viscosity of a conventional binder compound on the basis of bitumen and SBS, produced in the same manner (FIG. 1).

TABLE 1 Composition and properties of binder compounds produced on large scale. Quantity (w. %) SBS 10 9.8 Fatty acids 15 14.9 Pentaerythritol gum resin 35 34.5 CaCO₃ filler 40 39.4 Antioxidant 0 1.5 Properties Softening point (° C.) 75-90 89-109 Viscosity at 180° C. (Pa · s) 1416 8600 PEN at 25° C. ( 1/10 mm) 71 PEN at 60° C. ( 1/10 mm) 127 Cold flexibility (° C.) initial −27 after 7 d at 70° C. −24 after 28 d at 70° C. −24 after 28 d under UV −15

Example 6 Retention of Flexibility and Softening Point with Increasing Quantities of Filler

The cold flexibility and softening point (PEN 25° C.) were determined on binder compounds containing SBS polymer, fatty acids, pentaerythritol gum resin, antioxidant and different quantities of CaCO₃ filler. All binder compounds showed a high hardness while retaining a high cold flexibility and softening point. As a result these binder compounds were ideal for use in road surfacing amongst others.

CaCO₃ Cold PEN filler (w. %) flexibility (° C.) 25° C. ( 1/10 mm) 34 −28 101 36 −28 88 38 −27 89 45 −28 50 −28

Example 7 Roof Covering Membrane Comp Rising the Binder Compound According to the Present Invention

A roof covering membrane was produced with the following dimensions:

-   -   Thickness: 3 mm     -   Length: 7.27 m     -   Width: 1.1 m     -   Surface area: 8 m²     -   Roll weight: 32.5 kg

This roof covering membrane contained no bitumen and was largely based on renewable carbon molecules, which was an ecological benefit. For application on a roof, this roof covering membrane also needed to be heated less whereby application could be faster and cheaper than with bituminous covering membranes. 

1-8. (canceled) 9: A roof covering membrane comprising a binder compound containing, based on the total weight of the binder compound, a natural oil in a quantity of 14 to 19 weight percent, a polymer in a quantity of 4 to 17 weight percent and selected from the group consisting of styrene-butadiene-styrene (SBS), styrene-ethylene-butadiene-styrene (SEBS), styrene-isoprene-styrene (SIS), polyisobutylene (PIB), polyhydroxybutyrate, polylactide (PLA), polyolefin, polyamide, polyester, atactic polypropylene (APP), and isotactic polypropylene (IPP) and combinations thereof, wherein the polymer does not contain a functional group selected from a carboxylic acid anhydride group, a carboxylic acid group, and an epoxy group, and a resin in a quantity of 32 to 70 weight percent. 10: The roof covering membrane according to claim 9 wherein the resin quantity is 32 to 40 weight percent. 11: The roof covering membrane according to claim 9 further comprising an antioxidant in a quantity of 0.1 to 3 weight percent. 12: The roof covering membrane according to claim 9 further comprising an antioxidant in a quantity of 0.5 to 1.5 weight percent. 13: The roof covering membrane according to claim 9 wherein the resin is a natural resin. 14: The roof covering membrane according to claim 9 further comprising a filler in an effective quantity at a maximum of 65 weight percent. 15: The roof covering membrane according to claim 14 further comprising an antioxidant in a quantity of 0.1 to 3 weight percent. 16: The roof covering membrane according to claim 14 further comprising an antioxidant in a quantity of 0.5 to 1.5 weight percent. 17: The roof covering membrane according to claim 9 further comprising a filler in a quantity of 20 to 50 weight percent. 18: The roof covering membrane according to claim 17 further comprising an antioxidant in a quantity of 0.1 to 3 weight percent. 19: The roof covering membrane according to claim 17 further comprising an antioxidant in a quantity of 0.5 to 1.5 weight percent. 20: The roof covering membrane according to claim 9 further comprising a filler in a quantity of 32 to 40 weight percent. 21: The roof covering membrane according to claim 20 further comprising an antioxidant in a quantity of 0.1 to 3 weight percent. 22: The roof covering membrane according to claim 20 further comprising an antioxidant in a quantity of 0.5 to 1.5 weight percent. 